Field
Embodiments of the present invention relate generally to semiconductor substrate processing and, more particularly, to systems and methods for cleaning native oxide and residue from a substrate surface having III-V group containing materials.
Description of the Related Art
In the microfabrication of integrated circuits and other devices, electrical interconnect features, such as contacts, vias, and lines, are commonly constructed on a substrate using high aspect ratio apertures formed in a dielectric material. The presence of native oxides and other contaminants such as etch residue within these small apertures is highly undesirable, contributing to defect formation during subsequent film growth or metalization of the aperture and increasing the electrical resistance of the interconnect feature.
A native oxide typically forms when a substrate surface is exposed to oxygen and/or water. Oxygen exposure occurs when substrates are moved between processing chambers at atmospheric or ambient conditions, or when a small amount of oxygen/moisture remains in a processing chamber and/or transfer chamber. In addition, native oxides may result from contamination during etching processes, prior to or after a deposition process. Native oxide films are usually very thin, for example between 5-20 angstroms, but thick enough to cause difficulties in subsequent fabrication processes. Furthermore, native oxide may cause high contact resistance in source and drain areas and adversely increase the thickness of equivalent of oxide (EOT) in channel areas. Therefore, a native oxide layer is typically undesirable and needs to be removed prior to subsequent fabrication processes.
In conventional practice, NF3 and NH3 gas mixtures are often used to remove native oxide from a substrate surface, which typically is a silicon surface. As circuit densities increase for next generation devices, the widths of interconnects, such as vias, trenches, contacts, gate structures and other features, as well as the dielectric materials therebetween, have decreased to less than 20 nm in width. Different materials are constantly developed to provide better electrical performance in semiconductor devices as the device dimension shrinks. For example, Ge containing materials, III-V group materials or III-V group compounds, such as Ge, SiGe, GaAs, InP, InAs, GaAs, GaP, InGaAs, and InGaAsP, and the like, are getting more and more attention for use in source-drain, channel, gate structure, metal silicide, or other regions of semiconductor devices. However, conventional native oxide removal technique by dry etching cannot efficiently remove native oxide from these surfaces, since conventional techniques are typically designed to remove native silicon oxide layer, in which the silicon atoms are attacked by NH4F or NH4F.NF forming solid by-produce (NH4)2SiF6 and sublimated into vapor phase gas, which is readily pumped out of the processing chamber. In contrast, III-V group materials or III-V group compounds do not react with NH4F or NH4F.NF to form a vapor gas by-product or readily sublimated into gas phase by-product which can be pumped out of the processing chamber. Instead, the conventional fluorine cleaning techniques may undesirably generate particles or solid by-product after reacting with the III-V group materials or III-V group compounds, thereby adversely creating surface contamination or keep the native oxide intact, which may eventually lead to device failure.
Other conventional cleaning techniques for removing native oxides from a surface exist but generally have one or more drawbacks. Sputter etch processes have been used to reduce or remove contaminants, but are generally only effective in large features or in small features having low aspect ratios, such as less than about 4:1. In addition, sputter etch processes can damage other material layers disposed on the substrate by physical bombardment. Wet etch processes utilizing hydrofluoric or hydrochloric acid are also used to remove native oxides, but are less effective in smaller features with aspect ratios exceeding 4:1, as surface tension prevents acids from wetting the entire feature. In addition, conventional HF cannot remove natives of III-V group compounds.
Accordingly, there is a need in the art for methods of removing native oxides and residue from a substrate surface having III-V group containing materials.